Automatic cleanup of acquired synchronization objects takes place during extension
teardown. This means that if PHP prematurely terminates a script (e.g. script
execution time is exceeded), objects will not be left in an unknown state. The
only exception to this is if PHP itself crashes (e.g. an internal buffer overflow).

Unnamed synchronization objects don't have a lot of use outside of a multithreaded
scenario. Unnamed objects are more useful in conjunction with the pthreads PECL
extension.

注意:

Named objects require additional care to be used on all systems.
If an object is instantiated with a specific set of parameters, it must always
be instantiated with those parameters or the object will probably end up in an
inconsistent state until the next reboot or a system administrator cleans up
the mess.